The present invention relates to an optical-fiber gyroscope of the Sagnac type with a fiber-optic loop, as well as a 3.times.3 coupler, comprising three optically coupled fiber-optic guides, whereby a first fiber-optic guide of the 3.times.3 coupler is coupled to an optical radiation source and the two other fiber-optic guides of the 3.times.3 coupler are coupled on one end to one end of the fiber-optic loop and, on the other end, to a radiation detecting instrument.
An optical-fiber gyroscope of the above-mentioned type is known from U.S. Pat. No. 4,440,498. One of its remarkable features is its 3.times.3 coupler, which enables it to run in so-called phase quadrature, whereby the arrangement shows its greatest responsivity at an angle of rotation rate of .OMEGA.=0. This is contrary to optical-fiber gyroscopes with standard beam splitters, which were customary in the past. With increased responsivity, however, other negative interference effects become noticeable. As an example, fluctuations in the radiation source or variations inside the 3.times.3 coupler cannot be distinguished from a signal, which results from rotations of the optical-fiber gyroscope.